fix: update dependency slash to v3 (#17019)

Author: renovate[bot]

packages/gatsby-page-utils/package.json

@@ -27,7 +27,7 @@
     "glob": "^7.1.4",
     "lodash": "^4.17.15",
     "micromatch": "^3.1.10",
-    "slash": "^1.0.0"
+    "slash": "^3.0.0"
   },
   "devDependencies": {
     "@babel/cli": "^7.5.5",

packages/gatsby-plugin-mdx/package.json

@@ -45,7 +45,7 @@
     "remark": "^10.0.1",
     "remark-retext": "^3.1.3",
     "retext-english": "^3.0.3",
-    "slash": "^2.0.0",
+    "slash": "^3.0.0",
     "static-site-generator-webpack-plugin": "^3.4.2",
     "style-to-object": "^0.2.3",
     "underscore.string": "^3.3.5",

packages/gatsby-remark-images/package.json

@@ -15,7 +15,7 @@
     "mdast-util-definitions": "^1.2.4",
     "potrace": "^2.1.2",
     "query-string": "^6.8.2",
-    "slash": "^1.0.0",
+    "slash": "^3.0.0",
     "unist-util-select": "^1.5.0",
     "unist-util-visit-parents": "^2.1.2"
   },

packages/gatsby/package.json

@@ -120,7 +120,7 @@
     "shallow-compare": "^1.2.2",
     "sift": "^5.1.0",
     "signal-exit": "^3.0.2",
-    "slash": "^1.0.0",
+    "slash": "^3.0.0",
     "socket.io": "^2.2.0",
     "stack-trace": "^0.0.10",
     "string-similarity": "^1.2.2",